Most modem, mid-range to high-end disk storage systems are arranged as redundant arrays of independent disks (RAID). A number of RAID levels are known. RAID-1 includes sets of N data disks and N mirror disks for storing copies of the data disks. RAID-3 includes sets of N data disks and one parity disk. RAID-4 also includes sets of N+1 disks, however, data transfers are performed in multi-block operations. RAID-5 distributes parity data across all disks in each set of N+1 disks. At any level, it desired to have RAID systems where an input/output (I/O) operation can be performed with minimal operating system intervention.
In most modem RAID systems, application software issues a procedure call to a state driven I/O driver of the operating system to perform the I/O operations. The I/O driver then passes the call to the RAID system. Successful or unsuccessful completion of the I/O operation is signaled from the RAID system to the I/O driver, and then to the application via call-backs, e.g., procedure returns and interrupt signals.
Often, the RAID system is used as the core for a file server, or a large database. There, the RAID system must be able to interact with a number of different types of hardware platforms, e.g., end-user PCs and work stations, and compute, print, and network servers, and the like. Consequently, it is a major problem to ensure that the RAID system will work concurrently and reliably with a variety of different operating systems, e.g., UNIX, LINUX, NT, WINDOWS, etc. Key among those problems is to determine how to give the RAID system a process context in which to perform multi-block operations, such as generating parity in a RAID-5 set, or copying data in a RAID-1 set when thousands of blocks need to be processed with a single I/O operation. On-line expansion and RAID level migration also require a process context.
Because process contexts can have different states and different state transitions in different operating systems, it is difficult to make a generic RAID system operate reliably. Also, prior art RAID systems require that there be some process context in the operating system to perform a multi-block operation in the RAID system.
Therefore, it is desired to provide a RAID system that can operate with any operating system, or no operating system at all.